Clean up reaction bottom sheet

[tabeckers]

The current reaction bottom sheet uses a BottomSheetBehavior. It has a peek_height to allow it to be swiped up. Because we want the peekheight area to also be filled with reaction items, the bottom sheet has a height that is larger than the screen. The CoordinatorLayout in which it exists pops up above the screen border so the bottom sheet can slide up until the peek height area is above the screen. As a result the entire area we wish to display reactions in will be filled with reaction items.

Another issue is that the bottom sheet can be swiped down to be removed. If we detect a state change to STATE_HIDDEN, we simply push it back up again so the peek height area is visible again. If we don't do this, we aren't able to swipe the reactions up again after swiping down the peek area.

[tabeckers]

Note: the animation sometimes jumps.